The present invention relates to a polyglycerol fatty acid ester mixture of mono-, di- and polyesters of polyglycerols having a degree of polymerization of 2 to 8 and at least one saturated and/or unsaturated fatty acid; to a bath additive composition containing this polyglycerol fatty acid ester mixture; to the use of the polyglycerol fatty acid ester mixture, and to a process for preparing the polyglycerol fatty acid ester mixture.
It is already known to employ polyglycerol fatty acid esters and ester mixtures as surface-active compounds for the preparation and stabilization of oil/water and water/oil systems because of their lipophilic and hydrophilic properties. These polyglycerol fatty acid esters are non-defined partial esters of polyglycerols with saturated and/or unsaturated fatty acids, there being numerous possibilities for the preparation of emulsifiers and solubilizers having suitably balanced fat and water solubility. The HLB of polyglycerol fatty acid esters or ester mixtures depends on their composition. This is determined by the synthesis route, in particular by the type and ratio of the reactants and by the reaction conditions.
The preparation of surface-active compounds having very specific HLBs by esterification of polyglycerol with fatty acids, however, poses various problems.
On the one hand, the reaction mechanisms with respect to the selectivity of the esterification and the number of substitutions occurring on the polyglycerol basic skeleton are to date largely unknown, so the activity of the polyglycerol fatty acid esters as emulsifiers and solubilizers can neither be checked nor clearly predicted.
It is particularly difficult, therefore, to prepare products having very specific surface-active properties by esterification of mixtures of various glycerol oligomers with fatty acids, especially as mixtures of this type, due to the industrial processes for their preparation, frequently consist of a large number of different polyglycerols and a relatively greater or lesser amount of cyclic glycerol oligomers.
On the other hand, the hydrophilic and lipophilic properties of the polyglycerol fatty acid esters are determined by the esterified fatty acids, the polyglycerol basic skeleton and the degree of esterification. In this connection, the increasing hydrophilicity of the polyglycerols with increasing degree of polymerization, the specific surface activity of the fatty acids and fatty acid mixtures selected in each case as the esterification product, their solubility in the polyglycerol and the unusually high decrease in the HLB of the polyglycerol fatty acid esters or ester mixtures when using fatty acids having high molecular weights are particularly to be taken into account. Additionally, the esterification ratio is dependent on the Weight or molar ratios of the reactants employed, polyglycerol and fatty acid, to one another.
In the prior art, polyglycerol fatty acid esters having defined properties have been prepared until now by esterification under controlled conditions of very specific glycerol oligomers, such as, for example, triglycerol or tetraglycerol, preferably with the use of protective groups.
The use of polyglycerol mixtures as the esterification starting material is known, for example, from published German Patent Application No. DE 4,023,593. This document describes esterification of a polyglycerol mixture which not only has a wide distribution with respect to the glycerol oligomers contained in it, but which also, due to the process by which it is prepared, contains a relatively greater or lesser amount of cyclic polyglycerols. The esterification product according to published German Patent Application No. DE 4,023,593 is a non-liquid surfactant whose action as an oil-in-water emulsifier is unsatisfactory, particularly with respect to the HLB (hydrophilic-lipophilic balance) achieved and the stability of the emulsions prepared.
Ethereal, mineral and also fatty animal and vegetable oils are very difficult to emulsify and/or solubilize, and there is a need for emulsifiers and/or solubilizers Which can effectively emulsify and/or solubilize these oils. Past attempts to use polyglycerol fatty acid esters or ester mixtures to emulsify or solubilize such oils have yielded only unsatisfactory results.